1. Field of the Invention (Technical Field)
The present invention relates to methods of extracting lipids from biomass, and more particularly to extraction of lipids from wet algae.
2. Description of Related Art
The need for alternative energy sources to replace fossil fuels has motivated many researchers and policymakers to develop innovative research programs around the world. Development of biofuels for the transportation sector is one of those programs directed towards renewable fuels, and significant progress has been achieved in development of some renewable biofuels. Feed stocks derived from biomass are promising sources of energy as they are renewable and production of energy at the industrial scale could improve the economic prominence of both existing infrastructures and under-developed geographic resources. Biodiesel is best known among renewable fuels and is currently being produced from a wide variety of vegetable and plant oils. The implication of the utilization of vegetable oils to produce biodiesel has increased demand on the domestic markets and in some instances the production is often reduced due to scarcity of the oil. Algae have long had the attention of biofuel investigators as a new source of oil for biofuel production, since algae can produce more oil compared to other biofuel feed stocks in shorter periods of time and in smaller areas. Algae are photosynthetic organisms which utilize solar energy to grow and convert water and carbon dioxide into lipids and other metabolites. They also can be grown on waste water generated by the agricultural and food industry. Algae have been used as a source to produce a wide variety of natural products for the pharmaceutical, biomedical, and nutraceutical industries. Carbohydrates, polyunsaturated fatty acids (PUFAs), vitamins, minerals, and dietary fibers are some of the commercial products derived from algae other than oils. Development and marketing of these byproducts is crucial for sustainable production of algae biodiesel, and this strategy is widely known as “algal bio refinery”. Development of byproducts during the process has become a necessary consideration to produce sustainable biofuels.
Production of algae biofuels consists of four major steps: 1) Algae cultivation, 2) Harvesting, 3) Extraction, and 4) Conversion of oils into fuels. Many different methods have been demonstrated to produce biodiesel from microalgae. These processes involve drying of algal biomass and extracting oils with expeller press, solvent extraction, etc., and some researchers have used supercritical carbon dioxide (CO2) extraction of lipids to produce biofuels. The extraction of oils is the most energy intensive step among the four steps; it consumes nearly 85% of production energy in the dry extraction method. Dewatering (dehydration) is also an energy prohibitive step if the biomass is recovered with or above 20% biomass loading. Generally, it is preferable to use biomass loading between 7.5-20% for wet extraction. To reduce the energy consumption involved in extraction, wet processing methods have been explored to produce biofuels. Hydrolysis of algal biomass and conversion of hydrolyzed lipids through supercritical ethanol process and single step extraction and conversion of wet algal biomass by using supercritical methanol are examples of such methods. However, these processes are energy intensive, making the entire process less energy efficient.
In addition, to make the production of algal biofuels sustainable, valuable co-products should be recovered from the algal biomass before conversion. Chemical lysing of algae, while efficient, affects the condition of byproducts, sometimes rendering them unsuitable, for example, for consumption.
Embodiments of the present invention solve these problems by providing hydrothermal liquefaction (HTL) or subcritical water (SCW) extraction methods to extract lipids in a manner that does not detrimentally alter the production of co-products.